On The Non-metallic Inclusions In The Ni-based Alloys And Their Removing Technology

With the rapid development of aviation,aerospace,missile and electronic industrial technology,the requirements for Ni-based alloys are stricter,especially for thin wires. Not only chemical constitution and service performance are limited,but also inner and surface qualities are required.The quality of 4J43 alloy and Cr20Ni80 alloy wires produced by one alloy company is examined and compared with the same products at home and abroad.It is found that all the alloy composition is coincident with standard requirement.But there are a lot of non-metallic inclusions in these two alloys and these nonmetallic inclusions may be the main cause of crack and break in products.Few people investigated on the behavior of non-metallic inclusions in the Ni-base alloy wire so far.In the paper new electrolyte used for electrolyzing Ni-based alloys is invented. Both metallographic examination and electrolytic assay are used to study nonmetal inclusions in Ni-based wires produced by normal process.The sources of inclusions in alloys are analyzed and process optimizing experiments for 4J43 alloy and Cr20Ni80 alloy are applied.Good test results are gained recently.New neutral electrolyte is made up by mixing oxysalt,sodium chloride and citric acid, etc.New electrolyte can not only effectively extract nonmetal inclusions in Ni-based alloys but also can have other good characters,such as,temperature and PH value is invariable during electroanalysis,anode mud precipitation of garrulous shape is little, electroanalysis process is calm;garrulous precipitation mixed in inclusions in half transparent film is so little that can be easily cleaned & separated,and high harvest rate is acquired.The inclusions extracted keep their former morphologies well in alloy,thus improving the veracity of experiment.The main inclusions existed in two Ni-based alloys are deoxidation results in melting process.These deoxidation results,which are detained in alloys owing to incomplete floating off before pouring,are endogenesis impurity.Silicate,aluminate and their composite inclusions are composed of elements such as Al,Si,Ca,Mn,Mg,Ti,Fe,Ni and so on.These inclusions exhibit many shapes such as sphericity,tablet,strip and abnormal shape because of different inborn time,solidified condition and component.In these kinds of Ni-based alloys,big brittle macroscopic inclusions have the huge impact on the properties of alloys,especially the composite inclusions composed of Ti,Al,Fe in 4J43 alloy and Cr20Ni80 alloy.This kind of impurity is mainly titanic oxides or nitrides generated by oxidizing of titanium in smelting which exhibits abnormal acute angle with size of 20-300μm and higher rigidity,belonging to brittle impurity with low strain rate.Because a rather large difference existed between fragile inclusions and alloy matrix in deformability,uniformity and continuity of alloy matrix were destroyed during the processing and deforming,causing stress concentration,inducing tiny cracks generated in the edge between alloy matrix and inclusions.With the increase of strain force,the crack extended and macroscopic gap or fracture formed.4J43 alloy processed by medium frequency induction melting is treated by electroslag remelting used ternary acid residue system of CaF2-Al2O3-CaO in industrial experiment.The results show that the process of electroslag remelting is stable under acid residue system and thus can effectively decrease nonmetal inclusions in 4J43 alloy. The total amounts of nonmetal inclusions decrease about 40%than those of normal process withous remeltingand whose sizes are bigger than 50μm disappear.The sizes of inclusions are in the range of 0-20μm.Inclusions are mainly brittle inclusions such as composite impurity which is mainly composed by aluminate and titanium oxide (titanium nitride)with some alumina and femic oxide before remelting.But,inclusions are mainly plastic silicate after electroslag remelting.The reason is that nonmetal inclusions in 4J43 alloy have been wiped off and new inclusions are created during remelting process.Tensile strength and elongation improve greatly,but the expansion property varies very samall and all fit the requirement of the state standard.The following process show that the rate of finished products improveThe influence of bottom blowing argon of lidale on the effect of removing of inclusions for 2080 alloy is studied by industrial experiment.The results show that only proper blowing argon flux can gain good removing effect.When the argon flux is stronger than 3.5L/min,inclusions increase after blowing argon,especially big size inclusions.It is because that strong blowing flux conduce big air bubbles,arising big fluctuation and rolling residue of molten steel and farther oxidation also.When the argon flux is 3.5L/min,the removing effect is best,inclusions decreasing 23%, especially big size inclusions decreasing 12%,compared with normal process without blowing argon.The test results show that mechanical property and accelerated test lifetime improve greatly after bottom blowing argon and clients give the same results.